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BQ24773: BQ24773 ACOK not working Correctly

Rahul Surawase48
Expert 2395 points
Part Number: BQ24773

Hello TI, 
                  We are working on BQ24773, Observing issues in ACOK voltage 
1. At 99% (Monitor by using BQ27542) of battery charging state, ACOK voltage is drop to 3V (which require 3.3V to continue charging)
2. Because of ACOK changes, ACDET also change 2.9V to 2.846V (As per the observation) it's because of Input adaptor voltage change to 5V to 4.8V 
3. Whos affecting on ACOK voltage, how to stable the ACOK (Problem is observe at 99% of SOC otherwise there was no any variation in ACOK voltage) 
4. Also test with different pull-up resistor across the ACOK pin (10k and 4.7k), but there was no any change 
5. Because of this issues battery is not going charge 100%, Full battery capacity is 13200 and charging stop at 12900 nearby
6. at BQ27542 also observe that there was drastic changes cycle count, when i start one cycle with zero cycle count after completing one cycle cycle count goes to 32

how to resolve the issues or there was any related documents to understand and work on it stable down system 

Thanks, 
Rahul

  • 0
    TI__Genius 11850 points

    Hi Rahul,

    Why does the adapter voltage dip from 5 V to 4.8 V? This will cause ACDET to dip as well, since the ACDET voltage is stepped down from the adapter voltage by a resistor divider.

    Regarding ACOK, there are 2 states. ACOK can either be pulled HIGH to an external pull-up rail when a valid adapter is present, or ACOK can be pulled LOW by an internal FET inside the BQ24773. Based on your description, it sounds like ACOK stays at logic HIGH the whole time, but the pull-up rail voltage is dropping. Please share your schematic so I can check the ACOK pull-up.

    Best regards,

    Angelo

  • 0 in reply to Angelo Zhang87
    Expert 2395 points

    Hello Angelo, 
                           As per i mention before it's work properly till 99%, there are no adapter voltage and ACDET voltage change but when it's reach near at 99% of battery capacity, it's start that cycle charging and discharging the battery again and again battery not going to full

    please find the attachment for BQ24773 schematic file for reference   

    Thanks, 
    Rahul BQ24773.pdf

  • 0 in reply to Rahul Surawase48
    TI__Genius 11850 points

    Hi Rahul,

    Thanks for sharing the schematic. However, I'm unclear about the points below. Can you please clarify?

    • In your original post, you reported that the adapter voltage dips from 5 V to 4.8 V, ACDET dips from 2.9 V to 2.846 V, and ACOK drops to 3 V. However, according to your last reply, the adapter voltage and ACDET voltage do not change. Can you please clarify the behavior?
    • In your schematic, the ACOK pin is set by a 10k/10k resistor divider from a 3.3 V pull-up rail, so the ACOK voltage will be 1.65 V (during logic HIGH) or 0 V (during logic LOW). I don't understand how ACOK can be 3 V (as stated in your original post) unless the pull-up resistor value is different from the 10k shown in the schematic.

    If you are concerned that the ACOK voltage is too low, then I think you should be able to remove R47 from your schematic. This way, the ACOK pin voltage will be 3.3 V (during logic HIGH) or 0 V (during logic LOW). A base-emitter voltage of 3.3 V is still within spec for the BC847 transistor. Just make sure that R23 is large enough such that LED2 can handle the current flowing through it when the BC847 transistor is on.

    Best regards,

    Angelo

  • 0 in reply to Angelo Zhang87
    Expert 2395 points

    Hello Angelo, 
                             
    As i say,


    1. When battery capacity is reach at 99%, The adapter voltage dips from 5 V to 4.8 V, ACDET dips from 2.9 V to 2.846 V, and ACOK drops to 3 V. (Please note that, when battery capacity reach at 99% then this issues is occurred )

    2. Issues is observe at when battery capacity reach at 99%, when battery start charging 0 to 98% there was no any voltage change in ACDET and ACOK 

    3. In the schematic R47 is not mount, there is only R17 pull up are connected 

    4. R17 pull up resistor is 10K which we are using 

    5. there we observe one thing when R45 changes ACOK also change currently we are use R45 base resistor 100K then we get ACOK 3.3V

    6. R23 we are using 330Ohm, need to increase value as you mention..? why we need to R23 is large, what we need to set R23 ..?

    Thanks, 

    Rahul

  • 0 in reply to Rahul Surawase48
    TI__Genius 11850 points

    Hi Rahul,

    Rahul Surawase48 said:

    1. When battery capacity is reach at 99%, The adapter voltage dips from 5 V to 4.8 V, ACDET dips from 2.9 V to 2.846 V, and ACOK drops to 3 V. (Please note that, when battery capacity reach at 99% then this issues is occurred )

    Why does the adapter voltage dip from 5 V to 4.8 V? Can you please capture a waveform showing the adapter voltage, ACOK, PHASE, and VBAT on the same graph as the adapter dips down to 4.8 V?

    Rahul Surawase48 said:

    2. Issues is observe at when battery capacity reach at 99%, when battery start charging 0 to 98% there was no any voltage change in ACDET and ACOK 

    If the battery is only charging up to 99% capacity before the battery discharge/recharge cycles begin, then can you try setting your ChargeVoltage() register setting to a slightly higher value? This should allow the BQ24773 to charge the battery more fully.

    Rahul Surawase48 said:

    3. In the schematic R47 is not mount, there is only R17 pull up are connected 

    4. R17 pull up resistor is 10K which we are using 

    5. there we observe one thing when R45 changes ACOK also change currently we are use R45 base resistor 100K then we get ACOK 3.3V

    6. R23 we are using 330Ohm, need to increase value as you mention..? why we need to R23 is large, what we need to set R23 ..?

    Thanks for clarifying your schematic. Regarding 6), R23 acts as a current limiting resistor for LED2. Please make sure that R23 is large enough so that the current flowing through LED2 is within the LED's current rating. The current through the LED can be calculated using Ohm's Law. When the BC847 transistor is on, the current through the LED should be approximately I = V/R = (VBUS - LED2 forward voltage drop)/330.

    Best regards,

    Angelo